THE PRODUCTION OF HYBRIDS. 557 



by trustworthy experiments made by gardeners" and relied upon for the foundation 

 of "laws based upon facts"; theories are then built up upon them, and are copied 

 from one book to another. It becomes very difficult afterwards to get rid of such 

 propositions, especially if they afford support to the hypotheses of distinguished 

 savants. 



An instructive example of the kind of thing referred to is afforded by the 

 following statement which for a long time obtained currency in works on Botany: 

 "Hybrids resulting from the crossing of two species exhibit two forms, in each 

 case, according as the pollen employed in generating them belongs to the one or 

 to the other species." There are, of course, two ways in which a pair of species,, 

 which may be represented by the letters A and B, may be crossed. In one case the 

 pollen from A is transferred to the stigma in B, whilst in the other case the pollen 

 is taken from B and transferred to the stigma in A. Now, it has been asserted 

 that it is possible to determine from the form of the hybrid which of the two 

 parent-species supplied the pollen. The hybrid is said to resemble that parent more 

 closely from which the pollen was derived so far as its flowers are concerned, but 

 to show greater affinity to the fertilized stock in respect of its foliage. This is, 

 however, absolutely untrue. All careful experiments, made without prejudice have 

 pointed to the conclusion that it makes no difference to the forms, either of the 

 leaves or of the flowers, whether the pollen has been taken from the one parent-species 

 or from the other. Besides this, in most instances the approximation of the hybrid- 

 form to one or the other stock affects all parts of the hybrid plant in an equal 

 degree, and not the flowers or the foliage only. In the rare cases where a hybrid 

 has flowers more like those of one parent and leaves more like those of the other, 

 it is just as likely for one stock as the other to have yielded the pollen used for the 

 cross. 



But it would be a thankless task to attempt to correct all the hasty, careless, 

 and erroneous statements, past and present, and it will probably be of greater 

 utility to give a general survey of what has been ascertained concerning the form 

 and temperament of hybrids by impartial observers who have taken into account 

 all the concurrent circumstances, and have allowed for the sources of error inci- 

 dental to the experiments. 



The formation of a hybrid plant presupposes two stock-plants as parents which 

 have different properties and characters. A cross must take place between the two 

 — that is to say, the stigma of the one must be dusted with pollen from the other; 

 the pollen must put forth pollen-tubes and an effectual union between spermato- 

 plasm and ooplasm must be effected. For the sake of brevity, the plant from which 

 the pollen, and therefore also the spermatoplasm, is derived is called the paternal 

 stock or father-plant, and that which has its stigma dusted and its ooplasm ferti- 

 lized is called the maternal stock or mother-plant. As a plant's external marks and 

 characteristics, which are perceptible to our senses, are an expression of its internal 

 organization and of the specific constitution of its protoplasm, it may be assumed 

 that the plant-individual which owes its existence to the union of two protoplasts; 



